Momentum independent collective excitations in H₃Li₂OrO₆: evidence for proximity to a bond-disordered Kitaev spin liquid

The intercalated iridate H3LiIr2O6 is the only Kitaev compound absent of long-range magnetic order and frozen moments. However, disorder is fundamental to the physics of this material. Even in crystallographically pristine samples, hydrogen zero-point motion randomly modulates the strength of the exchange interactions. What remains to be understood is how such disorder can act to generate a ground state absent of any frozen moments but with low-energy collective spin excitations. Since disorder is prevalent among quantum materials H3LiIr2O6 stands as an emblem of a major and central challenge facing the field of quantum spin liquids: how are we to understand the ground states that arise from an interplay of disorder and quantum correlations? In this talk I will present resonant inelastic x-ray scattering measurements that address this challenge by revealing the full spectrum of collective excitations that characterize magnetic correlations in H3LiIr2O6. The result is striking for the complete lack of momentum dependence of an intense high-energy continuum of excitations signifying the predominance of quantum fluctuations on top of a disordered background. In light of our measurements, H3LiIr2O6 must be considered a new phase of disordered matter, distinct from a spin glass or paramagnet. The data support the interpretation of H3LiIr2O6 as a disordered topological phase in close proximity to the Kitaev quantum spin liquid.